Houseplant Care / Soil Mixes
When it comes to houseplant potting soil a big topic is aeration. How much is needed and what type? We have two soil recipes below that can be used interchangeably. The second recipe uses three different types of aeration while the first recipe combines the total amount of aeartion into just one ingredient to simplify the process.
Diversity in aeration inputs can be nice and they each have their intended reason but really the ultimate goal is to provide pockets of air for roots, prevent soil compaction and prevent overwatered/soggy soil. Perlite or Pumice are the most ideal for any potting soil and can be used exclusively. As you’ll notice below the simple soil recipe has an increased amount of perlite while excluding the chunky coir and bark altogether.
Biochar is optional, I use it in all my soil recipes at 5%-10% by volume and is available here on our website where you can read all about the benefits and why I don’t grow without it. :)
Updated Simple Organic Houseplant Soil Blend:
5 parts / 5gal sphagnum peat moss and/or coco coir
5 parts / 5gal perlite or pumice
2.5 parts / 2.5gal worm castings and/or compost
1 part / 1 gal biochar
Amounts below are per the Gallon measurement, 13.5 gallons total base soil mix as noted above, adjust as needed for the amount you make.
1 cup rock dust
1/2 cup kelp/alfalfa
Base houseplant blend:
Makes 25 Gallons, perfect to mix and store in a 45gal. storage tote. “Parts” are noted so one can adjust volume as needed but make sure to adjust the amount of soil amendments also.
2 parts or 5 gal 50/50 Canadian sphagnum peat moss
& coco coir
2 parts or 5gal perlite or pumice
2 parts or 5 gal quality compost or castings
2 parts of 5gal chunky coir
1 part 2.5 gal bark
1 part 2.5 gal biochar
1 cup rock dust
1 cup kelp / alfalfa
1 cup neem/Karanja
Anthuriums: Extra aeration! 2 or 3 parts Houseplant Soil to 1 additional part Aeration. Perlite, pumice, chunky coir, bark etc…
Hoya, Succulents, Cacti: 4 parts Houseplant Soil and 1 part Perlite, Pumice or Lava Rock.
Notes on Peat Moss vs. Coir
- If you are in North America I would suggest Canadian Sphagnum Peat Moss. In the rest of the world (South America, Asia, Australia, Europe etc) I would recomend coconut coir. This is in relation to reducing the distance the raw material has to travel to you. In regards to peat moss, Europe has a very long history of using peat to heat homes, as fuel, and peat bogs are greatly depleted, I would check the source of your peat and make sure you are comfortable with where it is coming from. In Canada the peat pogs are extensive, great environmental restrictions and guidelines are in place to not only prevent excessive harvesting but there is a limit to what can be harvested from one location and is then returned back to nature. It has been shown that more sphagnum moss grows each year than is harvest making it a renewable resource at the current rate of harvest.
- If using more than 50% of coconut coir it is suggested to add 1/2 cup gypsum (or other sulphur amendment) per cuF to account for the lack of S in coconut coir. Coconut coir is also lacking in soil bacteria/fungi and other nutrients that sphagnum moss contains. Good compost or castings will counteract this but it is something to take note of.
- Coconut coir is often touted as the sustainable option to peat but it is important to understand the extreme rate of growth coconut farming undertook in the last 20 years to satisfy the coconut oil/water craze. Many native rainforests were destroyed via slash n’ burn to acquire the land to grow the worlds coconut oil/water. Insecticides and salt-based fertilizers are used to farm coconuts while none are used in the harvesting of peat.
- “Canada has 113 million hectares (280 million acres) of peatlands, nearly one-quarter of the entire world’s production space. Of this, the industry, over its 60-plus years of activity, has used only 29,000 hectares (72,000 acres). This is .02% of the country’s peatlands.”
- In contrast there is currently about 12 million hectares of coconut in production, 12 million hectares of tropical ecosystems taken away to grow coconuts. That’s 413.8x more land dedicated to growing coconuts than of harvesting peat. None of the land being farmed for coconuts is being returned to its natural state.
- “Our use of best management practices to restore peatland is founded on the 30-plus years of research conducted by the University of Laval through the Peatland Ecological Research Group (PERG). This Group has developed, through peer reviewed research, a technique that will return the harvested peatlands to peat-accumulating ecosystems. Through the application of the moss layer transfer technique, the restored harvest sites:
• Have typical bog plant biodiversity cover established within three to five years following restoration and is dominated by sphagnum mosses
• Have organic matter values restored that are comparable to those of natural systems
• Have their water table rise quickly, improving hydrological conditions. Research suggests that it will take between 15 to 20 years to accumulate a thick enough moss layer that will again regulate the water fluctuations.
• Have carbon emission reduced and can return to net annual carbon sinks after a decade to 15 years post-restoration.”
- I live in California and have determend Canadian Sphagnum Peat Moss is the best option for me to create potting soil. I provide all of the above information not to persuade one to use this or that input but to hopefully provide better insight on the production of both products so that we can all make better informed decisions on what is best for our location.
- 70+ years ago, prior to the use of peat moss or coconut coir, pests, diseases and poor quality plants was often the result of digging up native soils and putting them into containers. If one wanted to grow plants in containers they would enter their local forests and waterways and find the best quality softest, lightest soil they could find which was often in and around creeks, watersheds, forests where years and years of decayed leaves accumulated. If we did not have access to Peat moss or coconut coir, we might have a more serious issue on our hands with over harvesting local ecosystems. The extent that people at home would be able to garden and grow plants indoors would certainly reduce. Every material we use in the modern world started as a raw natural material and energy/fuel was used to move it from it’s origin and into your home. Of all the raw materials we use I think those used for gardening, growing our own food and plants, improving the soil in and around our homes and communities is a positive use of natural resources and the more we can all collectively grow plants naturally without the use of synthetic fertilizers and pesticides the even greater positive impact we can create.
- If one lives in the right part of the world and has the patience….Leaf mould is an excellent substitute for peat and coir if you have access to it or the material and patience to make it. You woul essentially make a pile of fallen deciduous tree leaves in autumn and occasionaly turn it for 1-2 years and eventually it will be a lightweight, airy textured, rich humus similar to peat or coir. If, for example, I lived on property in the Northeast United States or Canada I would certainly make this a home project next to the kitchen compost pile! https://www.thespruce.com/making-and-using-leaf-mold-2539475
Notes on Perlite vs Pumice vs Scoria
There’s consideral confusion about Perlite & Pumice in particular and that’s interesting because all three are the same material, amorphous volcanic glass. :)
Also known as pearlstone, a natural glass and similar in composition to obsidian. Perlite is formed from the rapid cooling of viscous lava or magma. When crushed perlite is rapidly heated water held inside is converted to steam. Tiny bubbles form in the softened rock and perlite is expanded up to 20x its original size.
~5 million tonnes are produced annually with Greece, Turkey, Western US being the largest producers, alogn with Hungary, Italy and Georgia.
There has been many numurous studies done on perlite dust to ensure worker safety and despite common rumors there is no glass pieces in the dust that cut and is legally classifed as “nouisance dust.” Of course, if one is sensitive to dust in general they should wear a mask when mixing, but studies have shown it poses no harm.
Volcanic glass formed during explosive volcanic eruptions when highly gaseious liquid lava is ejected into water or air as a froth containing masses of bubbles and rapidly cools. Pumice is light enough to float on water and usually light in color. Found wherever volcanos are with 21 million tonnes commercialy produced each year with highest amounts in Italy, Turkey, Greece, Iran, Chile and also in western united states.
Mineral Comp. Pumice / Perlite
Silicon Dioxide: 76.2% / 70-75%
Aluminum Oxide: 13.5% / 12-15%
Ferrous Oxide: 1.2% / .5 - 2%
Sodium Oxide: 1.6% / 3-4%
Potassium Oxide: 1.8% / 3-5%
Calcium Oxide: 0.8% / .5 - 1.5%
Magnesium Oxide: 0.05% / .2-.7%
Many might be more familiar with the names “volcanic rock” as sold in big box stores or “cinder” sold very cheap in landscape yards. Scoriaceous basalt, as its full name, is the heaviest of the three and usually darker red, brown or black in color depending on location. Scoria is formed when gases in magma expand to form bubbles as lava reaches the surface. The bubbles are retained as the lava solidifies. There is greater variation in mineral composition of scoria because of its density but is also dominated by silicon dioxide like perlite and pumice.
Logistically speaking, pick whichever you prefer, whichever is convenient or local to you. Perlite is the lightest to handle and ship, pumice a pretty far second and scoria the heaviest. While it provides sufficient aeration it provides the least, but if purchased from a local landscape yard (ask for cinder) it can by far be the most cost effective option.
Worth noting: More than 50% of all Perlite, Pumice and Scoria is used in construction with horticultural use being one of the smaller categories of use behind other industries.
Fun Fact: LECA/Hydroton, or expanded clay (Haydite), was invented in 1917 when the clay was super heated to 2100F causing it to expand and become porous, it was this invention that later lead to the discovery of heating perlite to expand and become porous.